1. Field of the Invention
The present invention relates to an apparatus and method to improve the clarity of an image, and more particularly to an apparatus and method to improve the clarity of an image, which can prevent the degradation of the clarity of a display unit caused by deterioration of the contrast characteristic.
2. Description of the Related Art
Recently, with the development of display units made of new materials, an apparatus and software to improve the quality of an image have been developed hand-in-hand. The greatest effect on the recognition by humans of the quality of an image through eyesight is clarity of the image.
The representative display units, for example, PDP, LCD and projection TV, which have been developed to replace the conventional CRT-type display units, can be made to have a narrow, light and large screen. In the display units such as PDP, LCD and projection TV, however, the precision and clarity of output image signals are frequently degraded due to image noise, blurring, and the limitation of bandwidth of input signals.
FIG. 1 shows an apparatus to improve the clarity of images according to the conventional art.
As shown in FIG. 1, the apparatus 10 to improve the clarity of images according to the conventional art includes a maximum gradient value calculator 11 to set a window with a desired size to input image signals with respect to current pixels, and to calculate the maximum gradient value based on pixel values in the window, a threshold calculator 12 to calculate a threshold value corresponding to a magnitude of the maximum gradient value, a diffusion calculator 13 to calculate the amount of diffusion between a current pixel and adjacent pixels based on the calculated threshold value and a pixel difference between the adjacent pixels, and a pixel value converter 14 to output a pixel value by adding a product value of the calculated amount of diffusion and a gain value to the current pixel value.
The artifacts that cause a phenomenon of seemingly overlapped white-colored ripples around edges of an image are called ‘shoot artifacts’. The apparatus 10 to improve the clarity of images according to the conventional art can calculate a Y signal of the input image signals and the maximum gradient angle of Y value of peripheral pixels, and then can remove a shoot artifact such that the threshold value is calculated based on the maximum gradient angle. The difference between the peripheral pixels is diffused through a gain adjustment so as to change the Y signal of the input image signal. However, since the clarity improvement apparatus 10 changes the Y signal value of the input image signal in proportion to an edge magnitude, it is difficult to effectively remove the shoot artifact with respect to the edge element. Furthermore, there is a problem of barely removing a ringing artifact occurring in another step of improving the clarity.
Korean Laid-open Patent Publication No. 2001-084015 discloses an apparatus to improve image quality including a decoder to divide input image signals into luminance signals and color difference signals, and a processor to detect a magnitude of the color difference among the signals output from the decoder and to remove the color difference signal, if the magnitude of the color difference is not greater than a reference value. However, in using a luminance signal of the input signals, the apparatus needs to convert a color space, and effectively removes a shoot artifact with respect to only a small edge element. Further, the apparatus cannot effectively remove a ringing artifact, in which jagged or fuzzy lines are produced in the vicinity of sharp edges of a reconstructed image, occurring in another step of improving the clarity.